Light core laminated structure

ABSTRACT

This specification discloses a laminate structure having a multi-ply corrugated board core to which coating is applied in such a way as to prevent delamination. The core is made of core unit sections that are cut from a block in a direction to have the flute passages exposed through the top and bottom faces of each core unit section. Some of the flute passages of the core slope in one direction and others slope in the opposite direction at acute angles to the face of the core to which the coating is applied. The coating extends into the flute passages for a part of their length and thus forms an undercut key structure that locks the coating to the core unit sections. There can be no delamination unless these keys break or the flutes tear, and because of the large number of keys and flutes (which may be up to 40 to 50 per square inch), a strong connection is obtained. The structure is used for curved laminates such as fiberglass boat hulls, and in the preferred construction the core is made of sections of substantially greater length than width and disposed so that the curvature is in the direction of the width of the sections. Units can be originally cut with lengthwise curvature so that no bending is required.

ilnited States Patent Edward Wultowitz 29 Wells Ave, Congers, NY. 10920 [21] Appl. No. 716,371

[22] Filed Mar. 27, 1968 [45] Patented Oct. 26, 1971 [72] Inventor [54] LIGHT CORE LAMINATED STRUCTURE 7 Claims, 7 Drawing Figs.

Primary Examinerlohn T. Goolkasian Assistant Examiner-Joseph C. Gil Att0rney-Sandoe, Neill, Schottler & Wikstrom ABSTRACT: This specification discloses a laminate structure having a multi-ply corrugated board core to which coating is applied in such a way as to prevent delamination. The core is made of core unit sections that are cut from a block in a direction to have the flute passages exposed through the top and bottom faces of each core unit section. Some of the flute passages of the core slope in one direction and others slope in the opposite direction at acute angles to the face of the core to which the coating is applied. The coating extends into the flute passages for a part of their length and thus forms an undercut key structure that locks the coating to the core unit sections. There can be no delamination unless these keys break or the flutes tear, and because of the large number of keys and flutes (which may be up to 40 to 50 per square inch), a strong connection is obtained. The structure is used for curved laminates such as fiberglass boat hulls, and in the preferred construction the core is made of sections of substantially greater length than width and disposed so that the curvature is in the direction of the width of the sections. Units can be originally cut with lengthwise curvature so that no bending is required.

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LIIGIHIT CORE LAMIINATIED STRUCTURE BACKGROUND AND SUMMARY OF THE INVENTION Plate constructions such as panels, blocks, boat hulls and the like can be made much stronger for their weight if they are provided with hollow cores. Constructions are made with honeycomb cores consisting of light and low-cost cellulose materials, but the disadvantage of such constructions has been that they delaminate when subjected to severe conditions, for example: boat hulls immersed in salt water and subjected to repetitive straining by wave action.

This invention provides an improved method for constructing a laminated structure, and the method is especially intended for use with plastic structures having hollow cores. The outstanding advantage of the method is that it provides a laminated structure in which the plastic laminations are mechanically locked to the core in addition to the bond that is provided by the adhesive and chemical bonding properties of the materials.

The invention also provides a method for making a laminated structure by use of block units which are fitted together on a support in much the same manner as bricks are fitted together in building a masonry floor, and the block units are shaped so that the structure can conform to various curves including warped surfaces that are required for the construction of boat hulls. The outer laminate is applied after a core of blocks has been assembled on a mold form, and when the outer laminate is set, the structure is a unitary mass. The cost of labor and equipment for making it is less than that of previously known methods.

In addition to the method, this invention provides a new product. The preferred embodiment includes a hollow core that is made of multiply corrugated paper board bonded with waterproof adhesive when the product is to be used outdoors or under water, and with an outside resin laminate, such as woven fiber glass cloth with resin filler. The paper of the corrugated board can be coated to make the waterproofing for a highest quality product.

Any of the known methods for making corrugated board can be used and the only difference in the preferred core material of this invention is that the flutes of successive plies are at an angle to the edges instead of being parallel, as in conventional constructions. This will be more fully described in connection with the drawings. The expression adhesive as used herein denotes substances that connect parts by the usual adhesive action and those that polymerize after application to obtain a chemical bonding.

The resin used for outside laminations may be any of those used for making waterproof plastic panels and especially those used commercially for making fiber glass boat hulls.

One of the characteristics of curved panels or hulls of this invention is that the core is made of a plurality of individual core units or blocks fitted together side by side and end to end and locked together by bonding of their interfaces and by covering their ends with a laminate to hold them together.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWING In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:

FIG. 1 is a fragmentary view, partly broken away and in section, showing the construction of the corrugated board core of this invention;

FIG. 2 is a diagrammatic view, on a smaller scale, showing a multiply corrugated board block from which the core units of this invention are made;

FIG. 3 is a greatly enlarged, fragmentary sectional view taken on the line 3-3 of FIG. 2;

FIG. i is a reduced-scale view of the block shown in FIG. 2 and illustrating the way in which core unit sections are cut from the block;

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. II shows two plies of corrugated paperboard including a front ply 11 and a back ply 12. The ply 11 has a front panel 14 connected to a back panel 16, by a corrugated center 18. This is a conventional corrugated paperboard construction except that the corrugated center 13 has flutes 20 which slope toward the right as they extend downward, as indicated by the dotted lines.

The back ply 12 has a front panel M and a back panel 16' connected together by a corrugated center 18' having flutes 20. The flutes 20 slope to the left as they extend downwardly as indicated by dotted lines.

The flutes 20 and 20' preferably slope in opposite directions, i.e., one group slopes toward the right and the other toward the left of the vertical; but the invention can be made with the flutes sloping in the same direction provided they slope at sufficiently different angles from one another. The included angle between the different directions of slope of the flutes 20 and 211' is between 10 and and preferably between 20 and 45.

The panels 14 and 16 are secured to the flutes of the corrugated center 18 by adhesive, in accordance with conventional practice. Where the final laminate is to be subjected to water or substantial moisture. the adhesive used is a waterproof adhesive. For highest quality laminate, the panels 14 and I6 and the corrugated center 18 should be waterproof. Where paper is used, the paper can be coated with a waterproof coating. The confronting faces of the plies 11 and 12 are also secured together by adhesive, in accordance with conventional practicc.

FIG. 2 shows a block 24 made of nine plies of corrugated paper board; these plies being indicated by the reference characters 11a-11i. The construction of each of these plies is the same as that described for the ply ll of FIG. 1, and the flutes of alternate plies of the block 24 slope in opposite directions in the same relation as explained in connection with FIG. 1.

The corrugated centers of each of the plies Ila-Iii are indicated by the reference character 18 and the flutes by the reference character 20. The corrugated centers 18 and flutes 20 are exposed at the top of the block 24. At the sides of the block 24, however, the open ends of the passages through the flutes 18 are closed by a layer of filler 26. This filler is preferably a waterproof resin which is applied to the side of the block in a puttylike consistency and it is pushed into the flute passages for enough to form undercut keys in the flute passages for holding the filler 26 in place. All of the plies of the block 24 are then wrapped with a cover 28 which is preferably made of woven fiber glass cloth soaked with a plastic resin which polymerizes to form a firm shell around all four sides of the block 24. This cover or coating 28 is broken away in FIG. 2 for clearer illustration, but in practice it extends for the full height of the block 24. The flutes 20 are left exposed at both the top and bottom faces of the block 24.

FIG. 3 is an enlarged sectional view through the block 24. The adhesive connecting the flutes 20 to the front and back panels of the plies Ila-111' is indicated by the reference characters 30 and the adhesive connecting successive plies together is indicated by the reference characters 32.

After the cover or coating 28 has hardened, the block 24 is cut into core unit sections 34. This is preferably done by means ofa saw 36 (FIG. 4) or other cutting tool. The block 24 is preferably made of substantially greater width than thickness; and the core unit sections 34 which are cut from the block 24 are preferably made with a height which is less than either their length or width. This provides advantageous dimensions for making laminates which have curved or warped surfaces. For other laminates, the block 24 may have different dimensions and the core unit sections 34 may be cut with sides having different relations to their length and width.

The important consideration in determining the height of each core unit 34 is that the height of the core unit represents the thickness of the core. This follows from the fact that only the top and bottom faces of the core unit 34 have the flute passages exposed, and thus only the top and bottom faces are suitable for securing the inner and outer laminations to the core.

FIG. shows core unit sections 34 placed side by side on a support 38 having beams 40. This support 38 and the beams 40 comprise part of a mold 42 which may be for a boat hull or other curved object. The core unit sections 34 are placed with their long dimensions extending parallel to the axis of curvature of the support 38. This makes it possible to construct a core with the curvature of the mold 42 and without curving any of the core unit sections 34. Actually the core is not curved but made up of straight lines with changes in the directions of the lines at the confronting faces of the respective core unit sections 34; but the actual surface of the laminate, after covering the core unit sections 34 with an outer coating 44, can be smoothed to a continuous fair form. This coating 44 extends downward into tapered clearances between successive core unit sections 34. Where the tapered section opens toward the bottom, as in the case of the clearance 46, the coating material 44 is preferably applied to one or the other of the confronting faces of the core unit sections in sufficient amount to fill the clearance 46.

In order to obtain greater strength, the core unit sections 34 are placed in staggered relation to one another so that the ends of the core unit sections of one row are located approximately midway between the ends of the core unit sections of the new row, the relation being similar to that in building with bricks and cinder blocks.

Where the mold 42 has compound curvature, i.e., it consists of a warped section, the core unit sections 34 can be cut to shorter lengths to accommodate them to curvature in the direction of their lengths. In the preferred construction of this invention, the core unit sections are too stiff to bend to any short radius. However, it is a feature of the invention that core units of any curvature can be cut from the block 24, as indicated by the dotted lines 50in FIG. 4. By following the block 24 along the lines 50, a curved core unit section is obtained and curves of any desired radius, including irregular curves, can be made when the block 24 is originally out.

If the curvature of the mold 42 at some locations is sharp enough so that the straight core unit sections 34 provide very sharp changes in direction, the core unit sections can be shaped to some extent by sanding them to obtain a more nearly desired contour for the outer faces of the core units. When subjected to sanding, the core unit sections should be subsequently cleaned by an air blast or vacuum cleaner because the dust produced by the sanding impairs the grip which the outer laminate or coating 44 obtains on the core.

In the preferred construction, provision is made for preventing the coating 44 from penetrating further than necessary into the flute passages. This makes the construction more economical since there is no useful purpose served by filling up the hollow core with plastic coating material from the outer laminate 44. The penetration of the coating 44 into the passages provided by the flutes is limited by applying an inner coating 54 (FIG. 6) to the top and bottom surfaces of the core unit sections 34 before applying the outer laminate 44. In the construction shown in FIG. 6 there is an inner laminate 44 which can be applied to the constructions shown in FIG. 5 after the plastic 44 has hardened and the construction can be removed from the mold 42. If desired, the laminate 44 can be placed on the mold 42 before the core unit sections 34 are placed on the mold. This is satisfactory for some constructions and with molds of certain shapes, but it is undesirable if the mold is of a corrugated shape and any substantial manipulating and fitting of the core unit sections 34 is required.

In FIG. 6, the lines 56 represent breaks at which the section changes from one ply to the next successive ply. Thus the flutes 20 slope in different directions after each of the break lines 56. The coating material 54, which is applied to both the upper and lower end of each core unit section 34, is of the consistency of a thick putty which must be pushed into the flute passages and which will move down into these passages only as far as it is pushed by force. It will not move by gravity. The material 54 is preferably pressed down in the flute passages to a distance at least as great as the width of the flutes. It can be pushed down further but this is unnecessary.

When the coating 44 is applied, it fills the space in the flute passages above the material 54; and it will be apparent from FIG. 6 that this forms, in effect, undercut keys which make it impossible for the coating 44 to delaminate without either breaking off the key portion which is in the flute passage, or tearing the flute passage loose from the ply. If the flutes 20 which open through the tops of the plies, were parallel to one another, as in conventional corrugated paper board, then the coating material 44 could pull loose by merely sliding out of the flutes. The only protection against delamination would be the adhesion of the coating 44 to the sides of the flute passages. However, with the flute passages extending at different angles to one another, as shown in FIG. 6, there is no direction in which the coating 44 could move and slide out of the flute passages. It is mechanically locked into the flute passages in addition to being secured to them by adhesion.

In addition to the treating of the core to obtain a waterproof construction, as previously described, the core can be treated also to obtain rot-proof and flame-proof characteristics.

The preferred construction has been illustrated and described, but changes and modifications can be made and some features can be used in diflerent combinations without departing from the invention as defined in the claims.

What is claimed is:

l. A laminated structure including a core comprising a plurality of core unit sections disposed successively side by side for the length of said structure, each of said sections being made of multiply corrugated board having successive plies with a front panel connected to a back panel by a corrugated center, the flute passages of the corrugated center opening through the top surface of the unit section, each of said core unit sections having a flat cover on its opposite sides that are disposed side by side with adjacent sections and confronting and permanently bonded thereto, and an outside coating covering the top faces of the unit sections throughout the length of said structure and having a portion of the inside surface of the coating extending into the flute passages for a part of the length of said flute passages.

2. The laminated structure described in claim 1 characterized by the flat cover surrounding all sides of the unit sections except the top and bottom surfaces of said unit sections, the flute passages of each section being at an acute angle to the top surface of the section, and some of the flute passages of the core sloping in different directions from other flute passages so that the portions of the outside coating that cover the top faces of the unit sections and that extend into the flute passages lock the outside coating to the core by an undercut keying angle that prevents delamination of the coating from the core unit sections.

3. The laminated structure described in claim 2 characterized by there being both top and bottom coatings on the core, and both of said coatings being similarly locked to the core.

4. The laminated structure described in claim 3 characterized by the laminated structure being of curved surface contour and with individual core unit sections of much greater length than width, and with the core unit sections disposed side by-side and oriented in the structure so that their width is in the direction of curvature of the structure, and where there is compound curvature, in the direction of the curvature of smaller radius.

5. The laminated structure described in claim 11 characterized by said laminated structure being curved throughout a portion of its area, the individual unit sections being of substantially greater length than width, the top and bottom surfaces being curved about axes extending transversely of the length of the sections, and the flute passages of each ply of the corrugated board being parallel to the other flute passages of that ply.

ii. The laminated structure described in claim ll characterized by some of the plies of the corrugated board having their flute passages sloping in the opposite direction from the flute passages of adjacent plies, the difference in slope being greater than 5 and the coating having portions extending into the flute passages that slope in different directions so that the flute passages key the coating to the core unit sections.

'7. The laminated structure described in claim ll characterized by the structure being useful for curved laminates such as fiber glass boat hulls, the plies of the corrugated board being bonded to one another by a waterproofing agent, a fabric surrounding all sides except the top and bottom surfaces of the core unit sections, resin securing the fabric to the multiply material, waterproofing material coating the flute passages, the outside coating material penetrating into the flute passages for a limited length of the flute passages, and the outside coating material including fiber glass. 

2. The laminated structure described in claim 1 characterized by the flat cover surrounding all sides of the unit sections except the top and bottom surfaces of said unit sections, the flute passages of each section being at an acute angle to the top surface of the section, and some of the flute passages of the core sloping in different directions from other flute passages so that the portions of the outside coating that cover the top faces of the unit sections and that extend into the flute passages lock the outside coating to the core by an undercut keying angle that prevents delamination of the coating from the core unit sections.
 3. The laminated structure described in claim 2 characterized by there being both top and bottom coatings on the core, and both of said coatings being similarly locked to the core.
 4. The laminated structure described in claim 3 characterized by the laminated structure being of curved surface contour and with individual core unit sections of much greater length than width, and with the core unit sections disposed side by side and oriented in the structure so that their width is in the direction of curvature of the structure, and where there is compound curvature, in the direction of the curvature of smaller radius.
 5. The laminated structure described in claim 1 characterized by said laminated structure being curved throughout a portion of its area, the individual unit sections being of substantially greater length than width, the top and bottom surfaces being curved about axes extending transversely of the length of the sections, and the flute passages of each ply of the corrugated board being parallel to the other flute passages of that ply.
 6. The laminated structure described in claim 1 characterized by some of the plies of the corrugated board having their flute passages sloping in the opposite direction from the flute passages of adjacent plies, the difference in slope being greater than 5* and the coating having portions extending into the flute passages that slope in different directions so that the flute passages key the coating to the core unit sections.
 7. The laminated structure described in claim 1 characterized by the structure being useful for curved laminates such as fiber glass boat hulls, the plies of the corrugated board being bonded to one another by a waterproofing agent, a fabric surrounding all sides except the top and bottom surfaces of the core unit sections, resin securing the fabric to the multiply material, waterproofing material coating the flute passages, the outside coating material penetrating into the flute passages for a lImited length of the flute passages, and the outside coating material including fiber glass. 